173 research outputs found
Extrasolar Planets and Their Host Stars
In order to understand the exoplanet, you need to understand its parent star.
Astrophysical parameters of extrasolar planets are directly and indirectly
dependent on the properties of their respective host stars. These host stars
are very frequently the only visible component in the systems. This book
describes our work in the field of characterization of exoplanet host stars
using interferometry to determine angular diameters, trigonometric parallax to
determine physical radii, and SED fitting to determine effective temperatures
and luminosities. The interferometry data are based on our decade-long survey
using the CHARA Array. We describe our methods and give an update on the status
of the field, including a table with the astrophysical properties of all stars
with high-precision interferometric diameters out to 150 pc (status Nov 2016).
In addition, we elaborate in more detail on a number of particularly
significant or important exoplanet systems, particularly with respect to (1)
insights gained from transiting exoplanets, (2) the determination of system
habitable zones, and (3) the discrepancy between directly determined and
model-based stellar radii. Finally, we discuss current and future work
including the calibration of semi-empirical methods based on interferometric
data.Comment: 80 pages in SpringerBrief format containing a few blank pages, 16
figures, 1 table of all stars with high-precision interferometric diameters,
glossary of commonly encountered terms, SpringerBrief 2017, ISBN
978-3-319-61198-
Exoplanetary Transit Constraints Based Upon Secondary Eclipse Observations
Transiting extrasolar planets provide an opportunity to study the mass-radius
relation of planets as well as their internal structure. The existence of a
secondary eclipse enables further study of the thermal properties of the the
planet by observing at infrared wavelengths. The probability of an observable
secondary eclipse depends upon the orbital parameters of the planet,
particularly eccentricity and argument of periastron. Here we provide
analytical expressions for these probabilities, investigate their properties,
and calculate their values for the known extrasolar planets. We furthermore
quantitatively discuss constraints on existence and observability of primary
transits if a secondary eclipse is observed. Finally, we calculate the
a-posteriori transit probabilities of the known extrasolar planets, and we
present several case studies in which orbital constraints resulting from the
presence of a secondary eclipse may be applied in observing campaigns.Comment: 7 pages, 5 figures, 1 table; accepted for publication in PAS
Constraints on Secondary Eclipse Probabilities of Long-Period Exoplanets from Orbital Elements
Long-period transiting exoplanets provide an opportunity to study the
mass-radius relation and internal structure of extrasolar planets. Their
studies grant insights into planetary evolution akin to the Solar System
planets, which, in contrast to hot Jupiters, are not constantly exposed to the
intense radiation of their parent stars. Observations of secondary eclipses
allow investigations of exoplanet temperatures and large-scale exo-atmospheric
properties. In this short paper, we elaborate on, and calculate, probabilities
of secondary eclipses for given orbital parameters, both in the presence and
absence of detected primary transits, and tabulate these values for the forty
planets with the highest primary transit probabilities.Comment: 3 pages, 1 figure, 1 table; to appear in ASP Conf. Proceedings:
"Pathways Towards Habitable Planets" 2009, Barcelona, Spain (eds.: D. Gelino,
V. Coude du Foresto, I. Ribas
Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars
We present interferometric angular sizes for 12 stars with known planetary
companions, for comparison with 28 additional main-sequence stars not known to
host planets. For all objects we estimate bolometric fluxes and reddenings
through spectral energy distribution fits, and in conjunction with the angular
sizes, measurements of effective temperature. The angular sizes of these stars
are sufficiently small that the fundamental resolution limits of our primary
instrument, the Palomar Testbed Interferometer, are investigated at the
sub-milliarcsecond level and empirically established based upon known
performance limits. We demonstrate that the effective temperature scale as a
function of dereddened color is statistically identical for stars
with and without planets. A useful byproduct of this investigation is a direct
calibration of the scale for solar-like stars, as a function of
both spectral type and color, with an precision of K over the range and K for the range F6V -- G5V. Additionally, we provide in
an appendix spectral energy distribution fits for the 166 stars with known
planets which have sufficient photometry available in the literature for such
fits; this derived "{\tt XO-Rad}" database includes homogenous estimates of
bolometric flux, reddening, and angular size.Comment: Accepted for publication in Ap
Predicting Stellar Angular Diameters from , , , Photometry
Determining the physical properties of microlensing events depends on having
accurate angular sizes of the source star. Using long-baseline optical
interferometry we are able to measure the angular sizes of nearby stars with
uncertainties . We present empirically derived relations of angular
diameters that are calibrated using both a sample of dwarfs/subgiants and a
sample of giant stars. These relations are functions of five color indices in
the visible and near-infrared, and have uncertainties of 1.8-6.5% depending on
the color used. We find that a combined sample of both main-sequence and
evolved stars of A-K spectral types is well fit by a single relation for each
color considered. We find that in the colors considered, metallicity does not
play a statistically significant role in predicting stellar size, leading to a
means of predicting observed sizes of stars from color alone.Comment: 8 pages, 1 figure, accepted for publication in MNRA
Observational Window Functions in Planet Transit Surveys
The probability that an existing planetary transit is detectable in one's
data is sensitively dependent upon the window function of the observations. We
quantitatively characterize and provide visualizations of the dependence of
this probability as a function of orbital period upon several observing
strategy and astrophysical parameters, such as length of observing run,
observing cadence, length of night, transit duration and depth, and the minimum
number of sampled transits. The ability to detect a transit is directly related
to the intrinsic noise of the observations. In our simulations of observational
window functions, we explicitly address non-correlated (gaussian or white)
noise and correlated (red) noise and discuss how these two noise components
affect transit detectability in fundamentally different manners, especially for
long periods and/or small transit depths. We furthermore discuss the
consequence of competing effects on transit detectability, elaborate on
measures of observing strategies, and examine the projected efficiency of
different transit survey scenarios with respect to certain regions of parameter
space.Comment: 16 pages, 11 figures, 8 tables; accepted for publication in Ap
An Extinction Map and Color Magnitude Diagram for the Globular Cluster NGC 3201
Differential variations of up to mag on a scale of
arcminutes across NGC 3201 are presented in the form of an extinction map. This
map, created by calculating average values for stars in small
subregions of the field with respect to a fiducial region, greatly improves the
appearance of the CMD of the cluster. We describe how we implemented this
technique in detail with our data for NGC 3201. A comparison between our map
and that of the same region extracted from the COBE/DIRBE reddening maps
published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale
similarities between the two maps as well as smaller-scale features which show
up in our map but not in the SFD map. Several methods of determining an
zeropoint to add to our differential extinction map are presented.
Isochrone fitting proved to be the most successful one, but it produces an
average for the cluster which is smaller than previously published
values by . Finally, our results seem to support the statement
by Arce & Goodman (1999) that the SFD maps overestimate the reddening in
regions of high extinction.Comment: 19 pages, 12 figures, 1 table, accepted for publication in AJ (March
2001). Full resolution version may be obtained at
http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.pdf (PDF) and at
http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.ps.gz (PS
Observational Window Functions in Planet Transit Searches
Window functions describe, as a function of orbital period, the probability
that an existing planetary transit is detectable in one's data for a given
observing strategy. We show the dependence of this probability upon several
strategy and astrophysical parameters, such as length of observing run,
observing cadence, length of night, and transit duration. The ability to detect
a transit is directly related to the intrinsic noise of the observations. In
our simulations of the window function, we explicitly address non-correlated
(gaussian or white) noise and correlated (red) noise and discuss how these two
different noise components affect window functions in different manners.Comment: 8 pages, 6 figures; to appear in the Proceedings of the 249th IAU
Meeting: "Exoplanets: Detection, Formation and Dynamics" (Suzhou, China);
added referee's comment
- …